U.S. patent application number 09/779446 was filed with the patent office on 2002-02-07 for piezoelectric ceramic material.
Invention is credited to Ohbayashi, Kazushige, Takase, Masanori.
Application Number | 20020014196 09/779446 |
Document ID | / |
Family ID | 16847425 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020014196 |
Kind Code |
A1 |
Takase, Masanori ; et
al. |
February 7, 2002 |
Piezoelectric ceramic material
Abstract
A lead-free piezoelectric ceramic material is provided having a
large piezoelectric strain constant which exhibits low temperature
dependence. The piezoelectric ceramic material includes Ba, Bi, Na,
Ti, and O, in the molar ratio of: 0.997.ltoreq.Bi/Na.ltoreq.1.003,
and Ba/Bi=2x/(a-x) wherein 0.99.ltoreq.a.ltoreq.1.01, 0<x<a.
The piezoelectric ceramic material may be employed for producing
piezoelectric devices such as oscillators, actuators, sensors and
filters.
Inventors: |
Takase, Masanori;
(Inazawa-shi, JP) ; Ohbayashi, Kazushige;
(Nagoya-shi, JP) |
Correspondence
Address: |
LARSON & TAYLOR, PLC
1199 NORTH FAIRFAX STREET
SUITE 900
ALEXANDRIA
VA
22314
US
|
Family ID: |
16847425 |
Appl. No.: |
09/779446 |
Filed: |
February 9, 2001 |
Current U.S.
Class: |
117/1 |
Current CPC
Class: |
H01L 41/187 20130101;
C04B 35/4682 20130101 |
Class at
Publication: |
117/1 |
International
Class: |
C30B 033/06 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 1999 |
JP |
11-226581 |
Claims
What is claimed is:
1. A composition comprising: a piezoelectric ceramic material
comprising Ba, Bi, Na, Ti, and O and having molar relationships of
0.990<Bi/Na.ltoreq.1.01; and Ba/Bi=2x/(a-x) wherein
0.99.ltoreq.a.ltoreq.1.01, 0<x<a.
2. The composition according to claim 1, wherein said piezoelectric
ceramic material is represented by the chemical
formula:xBaTiO.sub.3-(a-x- )(Bi.sub.bNa.sub.c)TiO.sub.3,wherein b
and c satisfy the relation 0.990<b/c.ltoreq.1.01.
3. The composition according to claim 2, wherein x is between 0.05
and 0.5.
4. The composition according to claim 1, wherein said piezoelectric
ceramic material has: a piezoelectric strain constant,
d.sub.33.sup.20.degree. C., of at least 100.times.10.sup.-12 C/N at
20.degree. C.; and a temperature coefficient, d.sub.33t, of no
greater than 0.15%/.degree. C.
5. The composition according to claim 2, wherein said piezoelectric
ceramic material has: a piezoelectric strain constant,
d.sub.33.sup.20.degree. C., of at least 100.times.10.sup.-12 C/N at
20.degree. C.; and a temperature coefficient, d.sub.33t, of no
greater than 0.15%/.degree. C.
6. The composition according to claim 3, wherein said piezoelectric
ceramic material has: a piezoelectric strain constant,
d.sub.33.sup.20.degree. C., of at least 100.times.10.sup.-12 C/N at
20.degree. C.; and a temperature coefficient, d.sub.33t, of no
greater than 0.15%/.degree. C.
7. The composition according to claim 4,
wherein105.times.10.sup.-12<d.- sub.33.sup.20.degree. C.
C/N<150.times.10.sup.-12, and 0.05<d.sub.33t %/.degree.
C.<0.14.
8. The composition according to claim 5,
wherein105.times.10.sup.-12<d.- sub.33.sup.20.degree. C.
C/N<150.times.10.sup.-12, and 0.05<d.sub.33t %/.degree.
C.<0.14.
9. The composition according to claim 6,
wherein105.times.10.sup.-12<d.- sub.33.sup.20.degree. C.
C/N<150.times.10.sup.-12, and 0.05<d.sub.33t %/.degree.
C.<0.14.
10. The composition according to claim 4, wherein said temperature
coefficient, d.sub.33t, is derived from the
formula:d.sub.33t(%/.degree. C.)=(d.sub.33.sup.80.degree.
C.-d.sub.33.sup.20.degree. C.)/((80.degree. C.-20.degree.
C.).times.d.sub.33.sup.20.degree. C.).times.100,wherein
d.sub.33.sup.80.degree. C. is a piezoelectric strain constant at
80.degree. C.
11. The composition according to claim 5, wherein said temperature
coefficient, d.sub.33t, is derived from the
formula:d.sub.33t(%/.degree. C.)=(d.sub.33.sup.80.degree.
C.-d.sub.33.sup.20.degree. C.)/((80.degree. C.-20.degree.
).times.d.sub.33.sup.20.degree. C.).times.100,wherein
d.sub.33.sup.80.degree. C. is a piezoelectric strain constant at
80.degree. C.
12. The composition according to claim 6, wherein said temperature
coefficient, d.sub.33t, is derived from the
formula:d.sub.33t(%/.degree. C.)=(d.sub.33.sup.80.degree.
C.-d.sub.33.sup.20.degree. C.)/((80.degree. C.-20.degree.
C.).times.d.sub.33.sup.20.degree. C.).times.100,wherein
d.sub.33.sup.80.degree. C. is a piezoelectric strain constant at
80.degree. C.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a piezoelectric ceramic
material and, more particularly, to a lead-free piezoelectric
ceramic material which has a large piezoelectric strain constant
and whose piezoelectric strain constant exhibits low dependence on
temperature.
[0003] 2. Background of the Invention
[0004] The majority of conventionally mass-produced piezoelectric
ceramic materials are piezoelectric ceramic materials containing
lead and/or lead oxide, such as PT (lead titanate) and PZT (lead
titanate zirconate). However, firing of such lead-containing
piezoelectric ceramic materials necessarily involves evaporation of
lead oxide and similar related substances and this obviously has
adverse environmental effects. The treatment of lead or a lead
compound without producing adverse effects on the environment can
be carried out but at high cost, among other disadvantages.
Therefore, there has been keen demand for a lead-free piezoelectric
ceramic material.
[0005] Recently, (Bi.sub.0.5Na.sub.0.5)TiO.sub.3 (hereinafter
"BNT") and bismuth-lamellar compounds have become of interest as
lead-free piezoelectric ceramic materials. However, as compared
with a lead-containing piezoelectric ceramic material, such a
lead-free material has a small piezoelectric strain constant, the
strain of the material is small with respect to a voltage applied
thereto, and the voltage generated from the material is small with
respect to a stress applied thereto. Therefore, employment of such
a lead-free piezoelectric ceramic material is of limited value in
the production of an active element such as an oscillator.
[0006] Japanese Patent Publication (kokoku) No. 4-60073 B discloses
a piezoelectric ceramic material containing BNT as a component.
This publication discloses a new composition of lead-free
piezoelectric ceramic material. However, the piezoelectric strain
constant of the material disclosed in the publication is at most
99.times.10.sup.-12 C/N. Although the publication is silent about
temperature dependence of the piezoelectric strain constant, the
temperature coefficient of the piezoelectric strain constant of the
piezoelectric ceramic material must be nearly equal to zero, in
order for the material to exhibit consistent performance over a
wide temperature range.
BRIEF SUMMARY OF THE INVENTION
[0007] The present invention relates to a lead-free piezoelectric
ceramic material having a large piezoelectric strain constant. The
piezoelectric ceramic material of the present invention may be
employed for producing piezoelectric devices such as oscillators,
actuators, sensors, and filters. In an optimal embodiment, the
lead-free piezoelectric ceramic material has a large piezoelectric
strain constant which exhibits low temperature dependence.
[0008] According to one aspect of the invention, there is provided
a piezoelectric ceramic material containing Ba, Bi, Na, Ti, and O,
having molar relationships of 0.990<Bi/Na.ltoreq.1.01, and
Ba/Bi=2x/(a-x) wherein 0.99.ltoreq.a.ltoreq.1.01, and
0<x<a.
[0009] Further features and advantages of the present invention
will be set forth in, or apparent from, the detailed description of
preferred embodiments thereof which follows.
DETAILED DESCRIPTION OF THE INVENTION
[0010] As indicated above, according to one aspect of the
invention, the piezoelectric ceramic material contains Ba, Bi, Na,
Ti and O having the molar ratio of 0.990<Bi/Na.ltoreq.1.01
Ba/Bi=2x/(a-x) wherein 0.99.ltoreq.a.ltoreq.1.01 and 0<x<a.
When the aforementioned Bi/Na and Ba/Bi ratios fall outside the
above respective ranges, the piezoelectric strain constant of the
material tends to be small.
[0011] In accordance with a second aspect of the invention, the
piezoelectric ceramic material is preferably represented by the
following chemical formula:
xBaTiO.sub.3-(a-x)(Bi.sub.bNa.sub.c)TiO.sub.3. Optimally, the
piezoelectric ceramic material is a solid material and has a
perovskite-type structure. However, the ceramic material may have a
structure including a perovskite phase as a primary crystalline
phase. The ceramic material may also have a structure including
other crystalline phases, so long as the phases do not impair the
piezoelectric characteristics of the material. In the above
chemical formula, b and c satisfy the relation
0.990<b/c<1.01.
[0012] In accordance with a third aspect of the invention, the
quantity x in the above chemical formula is preferably within the
range of 0.05 and 0.5. When x is less than 0.05 or in excess of
0.5, the piezoelectric strain constant of the piezoelectric ceramic
material tends to be lowered. The lower limit of x is determined to
be 0.05, since the morphotropic phase boundary may exist in the
vicinity of the composition in which x=0.05 to 0.06. Therefore,
when x is less than 0.05, the piezoelectric strain constant of the
piezoelectric ceramic material decreases drastically, and thus
obtaining a large piezoelectric strain constant (e.g.,
170.times.10.sup.-12 C/N or more) may be difficult.
[0013] More preferably, x is between 0.1 and 0.5 inclusive, much
more preferably, between 0.2 and 0.5 inclusive. When x falls within
the above range, a notably large piezoelectric strain constant can
be obtained. In addition, temperature dependence of the
piezoelectric strain constant is reduced. When x falls within the
above range, the resultant composition contains a large amount of
barium titanate as a solid solution, as compared with the
composition in which the morphotropic phase boundary exists.
[0014] In accordance with a fourth aspect of the invention, when x
falls within the preferable range of the third aspect, the
piezoelectric ceramic material has a piezoelectric strain constant
at 20.degree. C. (d.sub.33.sup.20.degree. C.) as measured according
to EMAS-6100 (standards by Denshi Zairyo Kogyokai) of
100.times.10.sup.-12 C/N or more (usually 170.times.10.sup.-12 C/N
or less, preferably 100.times.10.sup.-12 to 160.times.10.sup.-12
C/N, more preferably 110.times.10.sup.-12 to 160.times.10.sup.-12
C/N).
[0015] A temperature coefficient of the piezoelectric strain
constant d.sub.33t is calculated on the basis of formula d.sub.33t
(%/.degree. C.)=(d.sub.33.sup.80.degree. C.-d.sub.33.sup.20.degree.
C.)/((80.degree. C.-20.degree. C.).times.d.sub.33.sup.20.degree.
C.).times.100. The temperature coefficient d.sub.33t is
0.15%/.degree. C. or less (usually 0.05%/.degree. C. or more,
preferably 0.08 to 0.12%/.degree. C., more preferably 0.08 to
0.11%/.degree. C.).
[0016] The values d.sub.33.sup.20.degree. C. and d.sub.33t can be
attained simultaneously. Briefly, when d.sub.33.sup.20.degree. C.
is 100.times.10.sup.-12 C/N or more (usually 170.times.10.sup.-12
C/N or less), d.sub.33t is 0.15%/.degree. C. or less (usually
0.05%/.degree. C. or more).
[0017] In accordance with a fifth aspect of the invention, the
piezoelectric ceramic material more preferably has
d.sub.33.sup.20.degree. C. of 105.times.10.sup.-12 to
150.times.10.sup.-12 C/N and d.sub.33t of 0.05 to 0.14%/.degree.
C., much more preferably d.sub.33.sup.20.degree. C. of
110.times.10.sup.-12 to 135.times.10.sup.-12 C/N and d.sub.33t of
0.08 to 0.12%/.degree. C.
[0018] Referring generally to all aspects of the invention
described above, the piezoelectric ceramic material preferably has
a large piezoelectric output constant (g.sub.33), as well as a
large piezoelectric strain constant. Accordingly, a piezoelectric
ceramic material having g.sub.33 of 18.times.10.sup.-3 to
21.times.10.sup.-3 V.multidot.m/N can be produced. Such a
piezoelectric ceramic material is applicable to production of an
active element or a passive element.
[0019] It will be understood that the piezoelectric characteristics
of a piezoelectric ceramic material can vary greatly with slight
changes in the amount of a particular component contained in the
material. In other words, even when a number of piezoelectric
ceramic materials contain the same elements, the piezoelectric
characteristics of the materials can differ greatly from one
another based on the different amounts of the elements contained
thereof and the different proportions of the elements.
[0020] The piezoelectric ceramic material of the present invention
contains constituents in proportions which are materially different
than those in previously available piezoelectric ceramic material.
Although the piezoelectric ceramic material disclosed in Japanese
Patent Publication No. 4-60073 contains the same elements as those
contained in the piezoelectric ceramic material of the present
invention, the proportions of the elements contained in the former
material differ from those of the elements contained in the latter
material. In particular, the amount of Ba contained in the material
of the present invention is greater than that of Ba contained in
the material disclosed in the publication. More specifically, the
amount of barium titanate contained in the material of the present
invention is greater than that of barium titanate contained in the
material disclosed in the publication. In addition, the material of
the present invention differs from the material disclosed in the
publication in that the material of the present invention contains
Na and Bi in substantially the same amounts.
[0021] In accordance with the first aspect of the invention
discussed above, there can be produced a piezoelectric ceramic
material which has a piezoelectric strain constant larger than that
of a conventional BNT piezoelectric ceramic material. In accordance
with the second through fifth aspects, there can be produced a
piezoelectric ceramic material which has a large piezoelectric
strain constant that exhibits low temperature dependence.
EXAMPLE
[0022] The present invention will next be described in detail by
way of examples. It will be understood that these examples are
presented not to limit the scope of the present invention but
rather to provide enhanced understanding of the present
invention.
[0023] (1) Production of Piezoelectric Ceramic Material and
Piezoelectric Element
[0024] Commercially available BaCO.sub.3 powder, Bi.sub.2O.sub.3
powder, Na.sub.2CO.sub.3 powder, and TiO.sub.2 powder were weighed
so as to attain the compositional proportions shown in Table 1.
These powders and ethanol were placed in a ball mill, and then
wet-mixed for 15 hours. The resultant slurry was dried in a
hot-water bath, and then calcined in air at 800.degree. C. for two
hours. Subsequently, the calcined product, an organic binder, a
dispersant, and ethanol were placed in a ball mill, and then
wet-mixed for 15 hours. Subsequently, the resultant slurry was
dried in a hot-water bath for granulation, and the granules were
formed into a column-shaped product having a diameter of 5 mm and a
thickness of 15 mm, through uniaxial pressing at 1 GPa. Thereafter,
the product was subjected to cold isostatic pressing (CIP) at 15
Gpa, and the resultant product was fired in air at
1,050-1,250.degree. C. for two hours, to thereby produce a
piezoelectric ceramic material. In Table 1, the samples marked with
an asterisk (*) fall outside the scope of the present
invention.
1 TABLE 1 Composition x a Bi/Na Test Example *1
Bi.sub.0.500Na.sub.0.500TiO.sub.3 0.000 1.00 1.000 2
Ba.sub.0.090Bi.sub.0.455Na.sub.0.455TiO.sub.3 0.090 1.00 1.000 3
Ba.sub.0.210Bi.sub.0.395Na.sub.0.395TiO.sub.3 0.210 1.00 1.000 4
Ba.sub.0.240Bi.sub.0.380Na.sub.0.380TiO.sub.3 0.240 1.00 1.000 5
Ba.sub.0.300Bi.sub.0.350Na.sub.0.350TiO.sub.3 0.300 1.00 1.000 6
Ba.sub.0.420Bi.sub.0.290Na.sub.0.290TiO.sub.3 0.420 1.00 1.000 7
Ba.sub.0.480Bi.sub.0.260Na.sub.0.260TiO.sub.3 0.480 1.00 1.000 8
Ba.sub.0.510Bi.sub.0.245Na.sub.0.245TiO.sub.3 0.510 1.00 1.000 *9
Ba.sub.0.005Bi.sub.0.495Na.sub.0.500TiO.sub.3 0.005 -- 0.990
[0025] Subsequently, the upper and lower surfaces of the produced
piezoelectric ceramic material were subjected to polishing. Then, a
silver paste was applied to both surfaces through screen printing,
and baking was carried out, to thereby form an electrode.
Thereafter, the electrode was subjected to polarization treatment
in insulating oil (silicone oil) maintained at 10-200.degree. C.,
through application of a direct current of 3-7 kV/mm for 30
minutes, to thereby produce a piezoelectric element.
[0026] (2) Measurement of Piezoelectric Characteristics
[0027] According to EMAS-6100, the piezoelectric strain constant
(d.sub.33.sup.20.degree. C.) and the piezoelectric output constant
(g.sub.33) of each of the piezoelectric elements produced in (1)
were measured in a thermostatic chamber maintained at 20.degree.
C., by use of an impedance analyzer (model: 4149A, product of
Hewleft Packard). The results are shown in Table 2.
[0028] Similarly, the piezoelectric strain constant
(d.sub.33.sup.80.degree. C.) of the piezoelectric element was
measured in a thermostatic chamber maintained at 80.degree. C. The
thus-measured d.sub.33.sup.80.degree. C. and the above-measured
d.sub.33.sup.20.degree. C. were substituted into formula (1), to
thereby calculate d.sub.33t. The results are also shown in Table 2.
In Table 2, the samples marked with an asterisk (*) fall outside
the scope of the present invention.
2 TABLE 2 d.sub.33.sup.20.degree. C. d.sub.33t g.sub.33
(.times.10.sup.-12 C/N) (%/.degree. C.) (.times.10.sup.-3 V
.multidot. m/N) Test Example *1 73 0.31 17 2 159 0.33 18 3 131 0.12
21 4 118 0.08 21 5 111 0.09 20 6 103 0.09 21 7 92 0.11 20 8 76 0.33
17 *9 64 0.30 15
[0029] As is apparent from Table 2, the piezoelectric elements of
Test Example 2 through 8 (i.e., the element of the present
invention), in which x falls within a range of 0.05 to 0.5, have
large piezoelectric strain constants (76.times.10.sup.-12 to
159.times.10.sup.-12 C/N). More particularly, in the piezoelectric
elements of Test Examples 3 through 7, wherein x falls within range
of 0.2 to 0.5, the temperature coefficient is as small as 0.08 to
0.12%/.degree. C. (i.e., the temperature dependence is low), and
the piezoelectric strain constant is as large as
92.times.10.sup.-12 to 131.times.10.sup.-12 C/N. In contrast, in
the element of Test Example 9 wherein the ratio by mol of Bi/Na is
0.990, the piezoelectric strain constant is small.
[0030] Again, the present invention is not limited to the specific
examples set forth above, and in accordance with purpose and use,
various modifications may be made within the scope of the
invention. For example, the piezoelectric ceramic material of the
present invention may contain Li and K as components. Li or K may
assume any form in the ceramic material, but these elements are
preferably substituted for some Na atoms contained in BNT. The
piezoelectric ceramic material of the present invention may
contain, in addition to the above components, other components or
unavoidable impurities, so long as they do not substantially affect
piezoelectric characteristics of the ceramic material.
[0031] Although the invention has been described above in relation
to preferred embodiments thereof, it will be understood by those
skilled in the art that variations and modifications can be
effected in these preferred embodiments without departing from the
scope and spirit of the invention.
* * * * *